The present invention relates to an automatic control device for a helicopter, as well as to an automatic control system comprising such an automatic control device.
It is known that an automatic control system for a helicopter generally comprises:
a set of sensors for automatically determining the effective values of state parameters of the helicopter;
means of adjustment allowing an operator of the helicopter to choose preset values of state parameters;
a set of actuators which act on control axes of the helicopter, according to control commands; and
an automatic control device which automatically determines control commands for said actuators, as a function of the state parameters and of the preset values, received respectively from said sensors and from said means of adjustment.
The job of the automatic control system is to aid, or even to completely replace, the pilot in the flying of the helicopter. For this purpose, it is capable of slaving one or more state parameters of the helicopter, such as the altitude, the attitude or the speed for example, to one or more preset values chosen beforehand by the pilot.
To do this, said automatic control device acts in a known manner:
on the cyclic axes (pitching axis, roll axis) and in general on the yaw axis. This case is referred to as xe2x80x9cthree-axisxe2x80x9d automatic control; and
optionally, also on the collective axis. This is referred to as xe2x80x9cfour-axisxe2x80x9d automatic control.
It is known that the two cyclic pitch channels (pitching axis, roll axis) produce a cyclic variation of the angle of incidence of the blades, the blades then having angles of incidence which vary as a function of their azimuth. This results in a tilting of the main forward motion and lift rotor of the helicopter, forward (pitching) or to the side (roll), or a combination of both these movements.
In the xe2x80x9cthree-axisxe2x80x9d configuration (pitch, roll, yaw) a mode with longitudinal-speed objectives and a mode with vertical objectives cannot be engaged simultaneously, since they are both based on pitchwise control, which can operate only one parameter at a time. Specifically, it is the pitching axis which, by operating the forward tilting of the rotor disk, makes it possible to control:
either a horizontal objective (airspeed for example), by virtue of the horizontal component of the aerodynamic resultant of the rotor disk (of the main forward motion and lift rotor of the helicopter);
or a vertical objective (vertical speed for example), by virtue of the vertical component of the aerodynamic resultant of said rotor disk.
In both cases, the power required for flight is, for its part, governed manually by the pilot by means of the collective axis. In a standard xe2x80x9cthree-axisxe2x80x9d automatic control device, a vertical mode of which is controlled pitchwise, it is therefore the pilot of the helicopter who must personally manage the power required for flight. Now, imperfect management may lead in this case:
to insufficient power, this culminating in a dangerous decrease in the airspeed (since the power is used first and foremost to maintain the preset of the vertical mode) which may become incompatible with the continuation of the flight; and
to excessive power, which culminates in an increase in the airspeed, which may even exceed the maximum permitted speed and thus cause damage to the helicopter.
The object of the present invention is to remedy these drawbacks. It relates to an automatic control device exhibiting increased safety in a totally automatic mode, with no intervention from a pilot, by maintaining the helicopter in an ever-safe flight envelope.
For this purpose, according to the invention, said automatic control device comprising at least one first objective law which corresponds to a vertical objective law in respect of the pitching axis, such an objective law being to bring at least one state parameter of the helicopter to an objective which represents a preset value of a state parameter, said objective law in respect of the pitching axis automatically determining for this purpose a control command for operating the tilting of the disk of said main rotor of the helicopter, is noteworthy in that it moreover comprises, in respect of the pitching axis:
at least one second objective law which corresponds to a speed limitation law which is intended for limiting the airspeed of the helicopter with respect to at least one limit value;
detection means for automatically detecting the reaching by the airspeed of said limit value; and
toggling means for, in order to select the objective law whose control command is used for the pitching axis, automatically toggling from said first law to said second law, when said detection means detect that the airspeed has reached said limit value.
Thus, by virtue of the invention, when a limit airspeed value is reached, said second law which is intended for limiting the airspeed is automatically engaged, this making it possible to remain under automatic control (without human intervention) and hence to remedy the aforesaid drawbacks, while maintaining the airspeed of the helicopter within a permitted domain of speeds. Of course, when the airspeed again deviates from the limit value, one returns automatically to the initial situation (consideration of the vertical objective law).
It will be noted that, within the framework of the present invention, an objective law is a means of calculation which determines a particular control command making it possible to bring or to bring back at least one state parameter of the helicopter to an objective (which represents a preset value of this state parameter or of another state parameter). Moreover, an objective law in respect of the pitching axis determines, automatically, for this purpose, a control command for operating the tilting of the disk of the main rotor of the helicopter.
Within the framework of the present invention said limit value of the airspeed may be:
either a maximum permitted airspeed;
or a minimum permitted airspeed.
However, in a preferred embodiment said detection means compare the airspeed (preferably directly) with respect to two limit values (upper and lower), namely the maximum permitted airspeed and the minimum permitted airspeed, and said second law is a law of protection of the airspeed envelope, which therefore protects both against low speeds and against high speeds.
The aforesaid characteristics of the invention relate to the case where the control of the collective axis is not accessible to the automatic control device (xe2x80x9cthree-axisxe2x80x9d automatic control).
In the case where the control of the collective axis is also accessible to the automatic control device (xe2x80x9cfour-axisxe2x80x9d automatic control), said automatic control device moreover comprises, according to the invention:
at least one objective law which corresponds to a vertical objective law in respect of the collective axis, this vertical objective law automatically determining a control command for operating the collective pitch of the blades of said main rotor of the helicopter; and
selection means which automatically select said vertical objective law, so as to use the corresponding control command in respect of the collective axis, when said detection means detect that the airspeed has reached said limit value.
Thus, by virtue of the invention, the vertical objective is achieved automatically by way of the collective axis (in this configuration), when the speed limitation law is active on the pitching axis.
Furthermore, in a particular embodiment, said automatic control device moreover comprises a holding-level law, detection means for automatically detecting leveling-off conditions and selection means for automatically selecting said holding-level law when said detection means detect leveling-off conditions, and doing so regardless of the objective law which is initially selected.
The present invention also relates to a system for the automatic control of a helicopter, of the type described above.
According to the invention, this automatic control system is noteworthy in that it comprises the aforesaid automatic control device.